Lavinia reviewed The Order of Time by Carlo Rovelli
Review of 'The Order of Time' on 'Goodreads'
4 stars
4.5 stars
What is time? What does it really mean to say that time ‘passes’? Do we exist in time, or does time exist in us? What is the meaning of now?
These are the questions that Carlo Rovelli tries to answer in The Order of Time. He takes us on a journey on how our understanding of the concept of time has changed from antiquity to the present and into the field of quantum gravity, his area of expertise. It is a magma of beautiful and exciting ideas, from physics to philosophy, “sometimes illuminating, sometimes confusing.”
We perceive time as one dimensional thing, it has a direction, the past is completely different from the future. The past seems to be one of the most obvious things, it is fixed, we have traces of it, we have memories, there are books to read and learn about the past. Time is …
4.5 stars
What is time? What does it really mean to say that time ‘passes’? Do we exist in time, or does time exist in us? What is the meaning of now?
These are the questions that Carlo Rovelli tries to answer in The Order of Time. He takes us on a journey on how our understanding of the concept of time has changed from antiquity to the present and into the field of quantum gravity, his area of expertise. It is a magma of beautiful and exciting ideas, from physics to philosophy, “sometimes illuminating, sometimes confusing.”
We perceive time as one dimensional thing, it has a direction, the past is completely different from the future. The past seems to be one of the most obvious things, it is fixed, we have traces of it, we have memories, there are books to read and learn about the past. Time is a great conceptual idea and works very well in our daily lives but is has a different meaning in quantum mechanics and general relativity. The elementary equations that govern the physical world fail to show any distinction between the past and the future.
Time is not a single thing, says Rovelli, but a multi-layered concept, a combination of properties that we can dismount, one by one. What it remains when you take away all these properties, is nothing at all. This is perhaps best exemplified by the physicists John Wheeler and Bryce DeWitt back in the 1970s, when they attempted to unify relativity and quantum mechanics resulted in time essentially disappearing completely from their equation (known as the Wheeler-DeWitt equation), suggesting that time does not exist at all.
Rovelli looks in detail at the nature of entropy, arguing that “what makes the world go round are not sources of energy but sources of low entropy. Without low entropy, energy would dilute into uniform heat and the world would go to sleep in a state of thermal equilibrium – there would no longer be any distinction between past and future, and nothing would happen.”
Boltzmann understood that entropy is not just a fundamental quantity but a measure of how things are disordered - when you mix thing (disorder) entropy goes up. The fact that entropy has been low in the past leads to an important fact that is ubiquitous and crucial for the difference between past and future: the past leaves traces of itself in the present. The only cause of the difference between past and future, argues Rovelli, is the low energy of the past.
This is an astounding idea that is hard to comprehend and perhaps even harder to accept. But it is also revealing, and told in Rovelli’s clear and concise style, makes perfect sense. Rovelli has a deep technical knowledge of his subject; at the same time, he writes beautifully and although I got lost several times when he discussed the strange world of loop quantum gravity, it was exciting to penetrate some layers of the mystery of time.
This is an exquisite and intellectually challenging book. It takes time to read, although, reflecting on the various physical variables of time, you might think otherwise.
link: my review
